Abstract
We studied the effects of anemia and ouabain administration on cardiac function and oxygen (O2) physiology in 9 newborn lambs. We measured O2 consumption (VO2), hematocrit (hct), heart rate, right atrial and aortic blood pressures and oxygen contents, the PEP/LVET ratio and left ventricular (LV)dP/dt; cardiac output (CO), systemic vascular resistance (SVR), systemic O2 transport (SOT) and the SOT/VO2 ratio were calculated. Following baseline measurements, lambs were made anemic (mean hct=12%) by isovolumic exchange transfusion with Plasmanate. Measurements were repeated prior to and 30 min. after administration of ouabain, 75 μgm/kg bolus followed by 0.05 μgm/kg/min. Anemia was associated with a heart rate related rise in LVdP/dt, a rise in VO2, increased CO, decreased SVR and a fall in the SOT/V 2 ratio. Following ouabain administration, VO2, CO and SOT fell, out LVdP/dt and the SOT/VO2 did not change. In this setting, ouabain effects are manifested primarily by alterations in O2 physiology variables, rather than by changes in left ventricular contractile function.
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